1. Field of the Invention
Apparatuses consistent with exemplary embodiments relate to a catheter (“endoscope” or “visualized catheter”) that has a mechanism for obtaining an image with the aim of providing an electronic visualized catheter using a solid state imaging element or confirming the insertion position, and in particular relates to the structure of an imaging part at the distal end of the insertion portion that is inserted into the interior of the observation object.
2. Description of Related Art
In order to observe the state of the interior of a body of a human or animal, or the interior of various machines and equipment, catheters are widely used. Catheters that are mainly used are those of a type involve inserting an image fiber in the interior of an observation object such as a living body and optically drawing out the image of the observation object region to the outside of the observation object to be observed (fiberscope type), and electronic ones that involve inserting a small solid state imaging element in the interior of an observation object, converting the image of the observation object region into an electric signal, drawing out that electric signal to the outside of the observation object, and observing the image with an external monitor.
As a solid state imaging element of the latter electronic visualized catheter, conventionally an image sensor having a CCD (charged coupled device) is often used, but recently an image sensor having a CMOS (complementary metal oxide semiconductor) has come to be used.
In a catheter that uses an image sensor including this type of solid state imaging element, the distal end portion that is inserted into the interior of an observation object, that is, the imaging part, is constituted to have, in addition to the solid state imaging element, an object lens system for forming an image of the observation object region on the light receiving surface of the solid state imaging element, and a circuit board (generally a printed circuit board) on which are formed conductor wiring layers such as an input signal line to the solid state imaging element, an output signal from the solid state imaging element, and a power potential line to the solid state imaging element.
Conventionally, as prior art documents of catheters that use an image sensor including this type of solid state imaging element, in particular, prior art documents relating to the structure of an imaging part, for example there are Japanese Unexamined Patent Application, First Publication No. H09-102896 (Patent Document 1) and Japanese Unexamined Patent Application, First Publication No. H04-218136 (Patent Document 2).
Patent Document 1 discloses a structure of the distal end portion of a catheter that uses a CCD image sensor as an imaging element, that is to say, the imaging part. FIG. 4 of Patent Document 1 discloses a structure in which, as the imaging part of the catheter, a lens barrel that houses the object lens is arranged on the front surface side (the side that should be made to face the observation object region) of a circuit board that has an opening hole, and a solid state imaging element is disposed on the back surface side of the circuit board (the surface on the opposite side with respect to the object lens system). In this structure, the outgoing light from the object lens system passes through the opening hole that is formed in the circuit board, and reaches the light receiving surface of the solid state imaging element.
In Patent Document 2, FIG. 3 and the like show a structure in which the circuit board is folded so as to form a U-shape, a solid state imaging element including a CCD image sensor is mounted on the outer side of the front surface thereof (corresponding to the bottom of the U shape), and an object lens system is disposed at a position separated from the light receiving surface of the solid state imaging element.
In the prior art mentioned above, since the object lens system is separated (placed at a distance) with respect to the light receiving face of the solid state imaging element, the image distance of the object lens system unavoidably increases. This means that, in order to obtain a wider angle of view, a lens of a glass material with a high refractive index, a small radius of curvature or a small diameter, and a concave surface is required, and means that the lens structure and processing become complex. Generally, in an endoscope or visualized catheter, a short object distance and a large angle of view are desired in order to observe the observation target region, particularly in a narrow lumen.
Also, since the object lens system is arranged separate with respect to the light receiving surface of the solid state imaging element, surrounding debris, bodily fluids and the like easily infiltrate the gap between the object lens system and light receiving surface of the solid state imaging element, and so there is a risk of these infiltrates exerting a bad influence during the observation.